1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display (LCD) device, and more particularly, to an LCD device having a high transmissivity.
2. Discussion of the Related Art
Recently, LCD devices have become widely used as a technology-intensive and value-added next generation device of due to its low power consumption, thin profile, and portability. Since the LCD devices including a thin film transistor (TFT) as a switching element, referred to as an active matrix LCD (AM-LCD) devices, have excellent characteristics of high resolution and display of moving images, the AM-LCD devices have come to be widely used.
In general, an LCD device is fabricated through an array process, a color filter process and a cell process. In the array process, array elements such as a TFT and a pixel electrode are formed on a first substrate. In the color filter process, color filter elements such as a color filter layer and a common electrode are formed on a second substrate. In the cell process, a liquid crystal layer is interposed between the first and second substrates.
FIG. 1 is a cross-sectional view of a related art LCD device. Referring to FIG. 1, the LCD device 1 includes a first substrate 10, a second substrate 20 and a liquid crystal layer 30 therebetween.
On the first substrate 10, a gate line and a data line are formed. The gate and data lines cross each other to define a pixel region P. A TFT Tr is formed at a crossing portion of the gate and data lines, and a pixel electrode 18, which is disposed in the pixel region P, is connected to the TFT Tr.
On the second substrate 20, a black matrix 25 including an opening, and shielding the gate line, the data line and the TFT Tr is formed. In other words, the black matrix 25 has a lattice shape. A color filter layer 26 including red, green and blue color filter patterns 26a, 26b and 26c are formed on the second substrate 20. The red, green and blue color filter patterns 26a, 26b and 26c are disposed in the opening of the black matrix 25 to correspond to the pixel region P. A common electrode 28 is formed on an entire surface over the black matrix 25 and the color filter layer 26.
The first and second substrates 10 and 20 with the liquid crystal layer 30 therebetwen are combined such that the common electrode 28 faces the pixel electrode 18 to obtain a liquid crystal panel 40. A seal pattern for preventing a leakage of the liquid crystal layer 30 is formed at edges of the first and second substrates 10 and 20. In addition, first and second alignment layers for determining an initial arrangement of the liquid crystal molecules of the liquid crystal layer 30 are formed.
First and second polarization plates 50 and 52 are formed at outer sides of the liquid crystal panel 40, respectively. Namely, the first polarization plate 50 is formed at an outer side of the first substrate 10, and the second polarization plate 52 is formed at an outer side of the second substrate 20. A backlight unit BLU for providing light toward the first substrate 10 is disposed under the first polarization plate 50.
Accordingly, when a signal of the data line is provided into the pixel electrode 18 through the turned-on TFT Tr, an electric field is generated between the pixel electrode 18 and the common electrode 28. The liquid crystal molecules are driven by the electric field, and the transmissivity of light from the backlight unit BLU is changed such that images are displayed.
As mentioned above, the first and second polarization plates 50 and 52, which are disposed at the outer sides of the liquid crystal panel 40, have perpendicular transmittance axes. The light from the backlight unit BLU is polarized into a first linearly-polarized light by the first polarization plate 50, and the first polarization light is changed into a second linearly-polarization light by the liquid crystal layer 30. The second linearly-polarized light passes through the second polarization plate 52 such that the light is incident to eyes of the user.
However, the first linearly-polarized light is incompletely changed into the second linearly-polarized light. Namely, the light provided onto the color filter layer 26 is scattered by pigments 27 of the color filter layer 26 such that parts of the first linearly-polarized light is changed into an elliptically-polarized light, and not the second linearly-polarized light.
Accordingly, the light incident to the eyes of the user is about 5 to 6% of the light from the backlight unit of the LCD device 1. Namely, a light efficiency of the LCD device 1 is very low.
FIG. 2 shows polarization conditions of lights from the backlight unit, the first polarization plate, the liquid crystal panel and the second polarization plate in the related art LCD device. Referring to FIG. 2, in the related art LCD device, the non-polarized light is emitted from the backlight unit BLU. The non-polarized light is changed to the first linearly-polarized light through the first polarization plate 50, and the first linearly-polarized light is changed into the elliptically-polarized light as well as the second linearly-polarized light through the liquid crystal panel 40 because of scattering by pigments 27 of the color filter layer 26 shown in FIG. 1. The elliptically-polarized light can not pass through the second polarization plate 52 such that transmittance and brightness of the LCD device is lowered.